The right of priority under 35 U.S.C. xc2xa7 119(a) is claimed based on German Patent Application No. 101 04 507.7, filed Jan. 31, 2001, the entire disclosure of which is hereby incorporated by reference.
The present invention relates to a method and system for controlling a compressor of a refrigerant circuit of an air-conditioning system of a motor vehicle.
The invention is based on the general problem that, in certain driving states, in which the vehicle engine has to produce a high power, for example, in the case of driving at high altitude or the case of sharp acceleration, the power output to the compressor of the refrigeration circuit of an air-conditioning system will be restricted. In the case of today""s air-conditioning systems, torque restriction caused by the driving situation is recognized, and the engine control device or the transmission control device completely shuts down the compressor. The instantaneous load torque is determined by a computer, with the aid of a function obtained by simulation and testing. It is possible for this function to depend on variables, such as high pressure of the refrigerant, compressor speed, activating rate of the set point, voltage of the blower motor of an air-conditioning device and the like.
A disadvantage of this known control system and method for limiting the load torque of the compressor is that a complete shutdown of the compressor takes place, with the result that the air-conditioning system cannot operate in the driving situations described. This leads to a loss in passenger comfort.
One object of the invention is, therefore, to provide an improved method and control system for controlling a compressor in an automotive air-conditioning system, such that the above-mentioned disadvantages can be avoided.
Another object of the invention is to provide an improved automotive air-conditioning system embodying the control system of the invention.
In accomplishing these and other objects, there has been provided in accordance with one aspect of the present invention a method for controlling a compressor in a refrigerant circuit of an air-conditioning system in a motor vehicle driven by an engine, comprising: determining an instantaneous load torque (M) of the compressor as a function (f) of at least one variable; determining a predetermined maximum limiting torque (Mlimit) as a function (f) of at least one variable and based on parameters set by a controller of the engine; comparing M with Mlimit, and if M greater than Mlimit; using an inverted function (finv) which is derived from function (f) to generate a control signal for the compressor based on Mlimit; and controlling the compressor based at least in part on the generated control signal.
In accordance with another aspect of the invention, there has been provided a control system for controlling a compressor in a refrigerant circuit of an air-conditioning system in a motor vehicle driven by an engine, comprising: a circuit for determining an instantaneous load torque (M) of the compressor as a function (f) of at least one variable, wherein function (f) is stored in a look-up table; a circuit for determining a predetermined maximum limiting torque (Mlimit) as a function (f) of at least one variable and based on parameters set by a controller of the engine; a comparator for comparing M with Mlimit; a circuit for generating, when M greater than Mlimit and using an inverted function (finv) which is a derivative of function (f), a control signal for the compressor based on Mlimit; and a control circuit for controlling the compressor based at least in part on the generated control signal.
In accordance with yet another aspect of the invention, there is provided a motor vehicle driven by an engine, comprising an air-conditioning system having a refrigerant circuit including a compressor, and a control system for controlling the compressor as defined above.
Further objects, features and advantages of the present invention will become apparent from the detailed description of several preferred embodiments that follows, when considered together with the accompanying figures of drawing.